Hollow fiber module

ABSTRACT

The invention relates to a hollow fibre separation module comprising an inlet ( 20 ) for the gas to be dried, an outlet ( 22 ) for dried gas, an access element ( 26 ) and a discharge element ( 28 ) for circulation gas, and a plurality of hollow fibres which respectively extend from the inlet ( 29 ) to the outlet ( 22 ) and comprise an inner region which communicates with the inlet ( 20 ) on one end of each hollow fibre, and with the outlet ( 22 ) on the other end of each hollow fibre. Said hollow fibres are wound up in a plurality of layers ( 40, 42, 44 ) to form a hollow cylindrical winding. Each layer ( 40, 42, 44 ) is inwardly defined by an imaginary cylinder ( 35, 36, 37 ) and has a number of hollow fibres which are wound onto said cylinder ( 35, 36, 37 ) in a helical manner with an alpha angle of inclination, are located at a distance a from each other, and are arranged on the cylinder in a homogeneously distributed manner. A layer ( 40 ) differs from an adjacent layer (e.g.  42 ) in that the fibres of one of the layers all form a plus alpha winding angle, whereas the fibres of the adjacent layers all form a minus alpha winding angle.

The invention relates to a hollow fiber fluid separation module forseparating gaseous or liquid fluids having an inlet for an inlet feedflow, an outlet for an exit flow, an access port for a permeate flow, adischarge port for the permeate flow, a module axis and a plurality ofhollow fibers, each of said fibers extending from the inlet to theoutlet and comprising an interior communicating with the inlet at oneend of each hollow fiber and with the outlet at the other end of eachhollow fiber. The invention relates more specifically to a hollow fiberdrier module to which a gas to be dried is supplied as the inlet feedflow, with the exit flow being dried gas and the permeate flow beingformed from a circulation gas. The hollow fluid separation module mayalso be operated in reverse, with the permeate flow flowing through theinteriors of the hollow fibers and with inlet and outlet communicatingwith the outer surfaces of the hollow fibers.

A hollow fiber drier module in which the hollow fibers are applied at anincline to the module axis and in a straight line on a porous tube isknown from U.S. Pat. No. 3,794,468 A. In a radial plane, the variousfibers of a respective one of the layers are offset between 2 and 10°relative to each other. All the fibers of one layer are parallel andintersect the hollow fibers of a neighbouring layer. The various hollowfibers are not wound around the winding body so as to form one at leastone winding, they instead extend between the end surfaces of a windingbody.

A hollow fiber fluid separation module that may also be utilized as adrier module is known from U.S. Pat. No. 5,837,033 A. The wind angle ofthe various fibers varies across the axial length.

Hollow fiber drier modules, in which the hollow fibers are helicallywound onto a coil carrier with no distance between the hollow fibers,are known from U.S. Pat. No. 5,702,601. Reinforcement filaments, whichare also wound onto the coil carrier, are utilized.

Hollow fiber fluid separation modules, more specifically hollow fiberdrier modules as they are substantially currently commercialized, have aplurality of parallel hollow fibers between inlet and outlet, with saidhollow fibers being arranged more or less evenly and extending in astraight line. In such type drier modules, the local density of thehollow fibers is not constant, more or less dense packings forminglocally. Although advantageous conditions are achieved for the gas to bedried, which flows in and out in the axial direction and from the inletin a substantially straight line toward the outlet, it is difficult tobring the circulation gas to homogeneously flow around all the outersurfaces of the hollow fibers. Further, the circulation gas finds itdifficult to spread evenly in a radial direction within the module.

In the hollow fiber fluid separation modules in accordance with thedocuments mentioned herein above, the modules are constructed fromregularly arranged hollow fibers; this allows avoiding locally more orless dense arrangements and the circulation gas to flow more evenlyaround the outer wall of the hollow fibers. A particularly advantageousconfiguration of the hollow fiber modules, more specifically of thedrier modules, is not achieved, though. In the prior art modules, thehollow fibers substantially extend in the axial direction. It is desiredto have modules the length of the various hollow fibers of which is atleast 1.5 times, more specifically three times, the axial length. Inspite thereof, these modules are to have a sufficiently strong winding,meaning it is to be made certain that the various hollow fibers will notbe capable of noticeably becoming displaced relative to one another. Inthe prior art modules, relative displacement is almost excluded sincethe hollow fibers are substantially extending between the end faces ofthe winding bodies and are not wound, as a matter of fact.

In view of the known hollow fiber modules, more specifically of thehollow fiber drier modules, it is the object of the invention toindicate a module that permits to achieve a strong winding, toaccommodate a great length of hollow fibers despite of the short overallaxial length of the module and to achieve an advantageous ratio betweenthe overall volume of the interior of all of the hollow fibers and theexterior surrounding of the hollow fibers.

This object is solved by a hollow fiber fluid separation module havingan inlet for an inlet feed flow, an outlet for an exit flow, an accessfor a permeate flow, a discharge port for the permeate flow, a moduleaxis and a plurality of hollow fibers, each of said fibers extendingfrom the inlet to the outlet and comprising an interior communicatingwith the inlet at one end of each hollow fiber and with the outlet atthe other end of each hollow fiber, with the hollow fibers being woundin multiple layers to form a hollow cylindrical coil, each layer beingdefined on its inner side by an imaginary cylinder and having a numberof hollow fibers helically wound on said cylinder with a helix angle.alpha., said fibers being in a clearance relationship a with each otherand equally spaced on the cylinder, with one layer differing from aneighbouring layer by the fact that all the fibers of the one layer areinclined at the wind angle plus .alpha. whereas all the fibers of theneighbouring layer are at the wind angle minus .alpha., each fiber beingwrapped 360° at least once around the associated cylinder and being laiddown during winding with a tensile strain high enough for the fiber tobe frictionally held in the best possible manner to the crosswisedisposed fibers lying underneath and low enough for the hollow fibersnot to have their inner cross section noticeably restricted even thoughthey are deformed at the intersections and for all of the hollow fibersto be applied with the same tensile strain.

In accordance with the invention, the flow around the fiber membranebundle is optimized on the side of the circulation air, meaning on theside of the permeate. In accordance with the invention, the discretehollow fiber membranes can be disposed relative to one another in such amanner that the module achieves maximum efficiency in making use of thewater vapour permeability of the membrane surface on the inner wall ofthe hollow fibers and in terms of its capability of absorbing watervapour of the circulation gas. Maximum efficiency is achieved when thepermeate flow is optimally guided around the outer walls of the membranefibers. For this purpose, the flow of the circulation gas must beoptimized. This has to occur with reference to the channel geometry andthe speed. The invention makes all this possible. It makes it possibleto uniformly distribute the circulation gas in a radial direction in anyradial plane along the module axis and to achieve good axial throughflow. The gas is advantageously circulated around the outer surfaces ofthe membrane fibers. The module may be optimized for respective purposesof utilization by varying the distance a and also by varying the windangle .alpha. Finally, the dimension of the hollow fiber can also bevaried, meaning both the inner diameter and the outer diameter, wherebythese changes can be made for each layer separately. Preferably, hollowfibers built according to the same design principle are used for onemodule, though.

The invention more specifically achieves a particularly strong windingof the membrane fibers. Since the membrane fibers are laid down at leastonce around the imaginary cylinder, there is a risk that the membranefibers become displaced, for example by mechanical action. As a result,the order of the winding is disturbed. Then, the flow around the fibersis not as uniform as initially achieved by the winding technique. Thesolution the invention offers here is to wind the hollow fibers withsufficient tensile strain. The tensile strain with which the hollowfibers are laid down during winding is high enough for the wound fibersto be frictionally held on the underlying fibers.

Mechanical loads cannot cause the hollow fiber to become noticeablydisplaced. On the other side, the tensile strain is low enough for thehollow fibers not to have their free inner cross section noticeablyrestricted at the intersections between a newly wound fiber and theunderlying fibers. At the intersections, the hollow fibers are slightlydepressed. The result is a strong winding. A slight registration fit isalso obtained.

The indications for the winding tension apply particularly to the hollowfibers from the second layer onward. As contrasted with the first layer,these hollow fibers no longer continuously fit against a cylinder, theynow merely rest substantially topically on the hollow fibers of theunderlying layer, with respect to which they are arranged crosswise.Accordingly, from the second layer onward, the hollow fiberssubstantially are only in punctual contact. At the points of contactwith the hollow fibers of the underlying layer, which they cross, slightimpressions are formed. From the second layer onward, the hollow fiberssubstantially are merely in punctual contact. The entire effect of thefiber tension is supported by the points of contact with the hollowfibers of the underlying layer, with the hollow fiber slightlydeforming. These deformations should not be so important as tonoticeably affect the free inner cross section, meaning to formdisturbing narrow passages therein.

A strong winding is obtained using the known winding method (see U.S.Pat. No. 5,299,749) in which the fibers are laid down in alternatinglayers at a positive wind angle (“s”-direction) and at a negative windangle (“z”-direction). The fiber tension is adjusted so that the load onthe hollow fibers at the points of contact with the neighbouring layersis kept within reasonable limits. Thanks to the distance betweenneighbouring hollow fibers of one layer, helically oriented channels areformed for the permeate flow, more specifically for the circulation gas.They communicate with corresponding helically oriented channels formedin the immediately neighbouring layers. This permits to have an axiale.g., undulating flow. This flow exists in addition to the helical flow.Both flows can be influenced and adjusted, also with respect to eachother, by selecting the clearance a between the hollow fibers of onelayer, the wind angle and the configuration, for example the geometry,of the hollow fibers. It is particularly important that a radialpermeability be generally obtained on the permeate side; thispermeability is also adjustable. It is also important because potting isperformed at the ends of each module. Free access to every single one ofthe hollow fibers in the structured winding permits to achieve selectivepotting, with all of the hollow fibers being sheathed.

The invention makes it possible to wind fibers around long, preparedwinding tubes, also referred to as preforms, that may be divided in aplurality of shorter modules later, after potting, at discrete selectivesites in the region of the potting. Very advantageous production andprocessing are thus made possible. Losses at the axial ends of thewinding resulting from reversing points and so on as they occur duringwinding no longer have the importance they had in manufacturing discretemodules and in directly producing discrete modules.

Preferably, the lower layer is laid down onto a tube that forms theimaginary cylinder of this layer. The winding thus has an improvedmechanical stability. A particular advantage thereof is that this tubecomprises radial passages that form the exit and access passages for thepermeate flow, more specifically for the circulation air. This exit oraccess is preferably formed in proximity to an axial end of the module.The associated access or exit is then preferably located in proximity tothe other axial end and preferably in the region of the outermost layer.The distance between neighbouring hollow fibers of one layer and thealternating sign of the wind angle from one layer to the other permitsto achieve on the one side good axial penetration of the permeate flowand on the other side good axial flow of the permeate flow. Overall, oneobtains a favourable flow path, more specifically counterflowcirculation of the permeate volume flow with respect to the fluid flowpath in the hollow fibers. Circulation around the outer surfaces of thehollow fibers is substantially equal and uniform.

In a preferred embodiment, the wind angle ranges between 15° and 75°,preferably between 20° and 70°, and more specifically is on the order of45°. The wind angle is defined by the angle at which the hollow fiber isinclined to the module axis when being wound around the imaginarycylinder; Put another way, the wind angle is the angle of a tangent of ahelically wound hollow fiber membrane with respect to the module axis.At an angle of 90°, winding would result in rings, at a wind angle of0°, the hollow fibers would be oriented parallel to the module axis onthe imaginary cylinder. The larger the wind angle, the longer thediscrete fibers and the lower the number of fibers that can beaccommodated in one layer. The same applies in reverse for small windangles. At large wind angles, one is confronted with the problem ofkeeping the distance between the hollow fibers within a desired rangebecause of the low number of hollow fibers in each layer.Advantageously, the distance between neighbouring hollow fibers rangesbetween 0.2 and 2 mm, more specifically from 0.3 to 1.2 mm. In thiscase, the hollow fibers typically have an outer diameter of about 0.6 mmand an inner diameter of about 0.3 mm. The hollow fibers are not limitedby outer and inner diameter; the outer diameter may for example rangefrom 0.1 to 5 mm.

In accordance with the invention, semi-permeable membranes e.g., hollowfiber composite membranes are utilized. Thanks to the winding technique,the inner cross sections are affected to the least possible extent overthe length of the fibers. The points of touching contact betweendiscrete hollow fibers are only located between neighbouring layers; thediscrete hollow fibers of one layer are not in touching contact with oneanother. The points of touching contact occupy but a very small fractionof the entire outer surface of the hollow fiber membranes so that a verysmall portion of the overall outer surface only is not available foraccess of circulation gas.

In a preferred developed implementation, the outermost layer is coveredby a shell that tightly surrounds said outermost layer and comprisesaccess or exit means for the circulation gas; these means are preferablylocated in proximity to an axial end region of the module. It has beenfound that what is termed a shrinkable tube is preferred to be used assaid shell. An oversized tube is pulled onto the finished module andheat shrunk in such a manner that it rests onto the uppermost layer witha tight but not compressive fit. The hollow fibers of the uppermostlayer are not compressed. The shell prevents circulation gas from beingshort-circuited past the outermost layer and outside of the outermostlayer. The tube onto which the innermost layer is wound has the sameaction with regard to a direct passage of circulation gas beneath thefirst layer that would be possible but for said tube.

Preferably, a plurality of hollow fibers, for example three, five fibersor more, is laid so that the fibers are parallel to one another, asactually known from U.S. Pat. No. 5,702,601 A. The total number n offibers one layer is capable of accommodating cannot be exceeded.

Other features and advantages of the invention will become more apparentupon reviewing the appended claims and the following non restrictivedescription of embodiments of the invention, given by way of exampleonly with reference to the drawing. In said drawing:

FIG. 1: is a perspective view of a drier module,

FIG. 2: is a sectional view of a complete filter having a module of theinvention that is only shown schematically herein,

FIG. 3: is a side view of a drier module having a winding core and threelayers, with a portion of the various layers cut away to betterillustrate the build-up of the layers,

FIG. 4: is a schematic side view of a winding core onto which a firsthollow fiber of a first layer is laid down to illustrate the windingprocess,

FIG. 5: is a view like FIG. 3, with a second hollow fiber being now laiddown,

FIG. 6: is a view like FIG. 3 after the third hollow fiber has beenwound,

FIG. 7: is a view like FIG. 3, with two hollow fibers being concurrentlywound in one working step,

FIG. 8: shows a portion of FIG. 6, meaning an intermediate state in theprocess of producing the entire winding,

FIG. 9: is a sectional front view of the intermediate state of FIG. 8,

FIG. 10: is a sectional view like FIG. 9, with the first layer havingbeen completed and with hollow fibers of a second and of a third layer,

FIG. 11: shows the encircled portion of FIG. 8 to an enlarged scale,

FIG. 12: is a sectional view taken along section line XII-XII of FIG. 8,

FIG. 13: is a front view of a module during manufacturing and of aportion of a winding device to illustrate the winding process,

FIG. 14: is a top view onto the arrangement of FIG. 13,

FIG. 15: is a sectional view of a portion of a winding, said sectionalview being approximately obtained following the section line XV-XV ofFIG. 3, but at a wind angle of about 45°,

FIG. 16: is a side view of a portion of a preform for a plurality ofmodules.

The hollow fiber module will be explained herein after by way of examplefor a hollow fiber drier module although the explanations given hereingenerally apply to any hollow fiber module.

The hollow fiber drier module has an inlet 20 for a gas to be dried andan outlet 22 for dried gas. Both are located at axial end regions. Inthese axial end regions, only the fiber interiors are freely accessible,the outer shells of the fibers are potted in a plastic material withoutthe spaces between the hollow fibers being axially accessible.Corresponding plastic rings 24 are shown.

Circulation gas is radially supplied to the module; for this purpose, ithas an access port 26, and a discharge port 28 for circulation gas. Themodule has a module axis 30. Finally, the module shown in FIG. 1 alsohas a winding core in the form of a tube 32 and an outer shell 34 in theform of a heat-shrinkable tube that is so short that there remains anuncovered region between the heat-shrinkable tube and the plastic ring24 through which the discharge ports 28 are realized, see FIG. 1. Theaccess port 26 is formed as follows: on the inner shell of the module,the tube 32 has a groove 27. Said groove is located in proximity to theassociated plastic ring 24 on the outer side of the tube 32. Further, atleast one axial bore 29 is formed from the end side of the tube 32thereinto, with said axial bore 29 meeting the groove 27. A plurality ofaxial bores 29 can be provided. Their number and/or inside diameter ischosen so that the desired quantity of circulation air is allowed topass. A regulatable valve can also be mounted upstream of the axial bore29. Together with the groove 27, the at least one axial bore 29 formsthe access port 26.

FIG. 2 shows the module mounted in a filter, but in a simplified view,with the hollow fibers passing therethrough in a straight line. Thefilter housing itself is known and needs not be discussed in detailherein; the reader is referred to the filter housing as disclosed inPCT/DE 01/02168 for example. As is evident from FIG. 2, the air entersthe filter housing through an entrance (see arrows) and reaches theinlet 20 of the filter module. The air to be dried flows through thehollow fiber membranes that remove humidity from the air. At the outlet22, it exits the module and flows inside the tube 32 to an exit port ofthe filter housing. Passages that are disposed in the region of anaccess port 26 are thereby provided in the tube 32. A fraction of thedried air flows through the passages in the direction counter to that ofthe air to be dried and exits in the region of the discharge port 28,see arrow.

The special winding method will be discussed herein after. The objectiveof the winding method is to obtain a hollow cylindrical coil havingmultiple layers. FIG. 3 shows a three-layer winding on a tube 32. Forbetter understanding of the build-up of the windings, portions of thediscrete layers have been cut away in steps; the complete three-layerwinding is only shown to the left in the FIG. It can be seen that thefirst layer 40 in the form of a multiple-start thread is formed by anumber n1 of hollow fibers. The hollow fibers are arranged in aspaced-apart relationship, the distance is indicated at a (see FIG. 8).The distance a is the same for all the spaces between the fibers of onelayer. In another layer, a may be different but is the same for all thespaces of this very layer.

Further, the number n of hollow fibers is different in each layer.Generally, the number increases with the number of layers, from thefirst to the second and so on. The fibers of one layer are not intouching contact with one another. They however are in touching contactwith the fibers of a neighbouring layer that are laid crosswise withrespect to those. In all the layers, the absolute value of the windangle is constant. The wind angle .alpha. changes sign from one layer tothe other. The first and the third layer 42 in FIG. 3 for example havethe wind angle plus .alpha. whereas the second winding comprises thewind angle minus .alpha. Accordingly, the first layer 40, which isdefined on the inner side by the cylindrical outer shell of the tube 32,has n1 hollow fibers with the clearance between said hollow fibers beinga1 and the helix angle plus .alpha. The second layer 42 has n2 hollowfibers with the clearance a2 and the helix angle minus .alpha. In thethird layer, n3 hollow fibers have a clearance a3 and a helix angle plus.alpha. This applies in equivalent fashion to higher layers. The secondlayer 42 is defined by an imaginary cylinder the diameter of which islarger by 2 d than the diameter of the tube 32, with d being the outerdiameter of the hollow fibers. For the third layer, the outer diameterof the imaginary cylinder is the diameter of the tube 32 plus 4 d.

From FIG. 4 it can be seen that helically oriented channels 38 remainfree between the discrete hollow fibers. They can also be seen forexample on the second layer 42 together with the underlying,intersecting, overlapped helical channels 38 of the first layer 40.Accordingly, the helical channels 38 of neighbouring layers arecommunicating. In addition to the helical flow path within one layer, amore or less axial e.g., undulating flow takes place making use of theintersecting helical channels 38 of neighbouring layers.

The sequence of laying the hollow fibers onto a winding core in the formof a tube 32 is evident from the FIGS. 4-6. In a winding machine, whichis actually known and needs not be illustrated herein, the tube 32 isclamped and rotated about its axis, meaning about the module axis 30,see rotation arrows. Simultaneously, an endless hollow fiber is suppliedat the wind angle .alpha. and laid down; in this manner, a first hollowfiber 54 is laid onto the winding core, with the result thereof beingshown in FIG. 4.

At the two axial ends of the winding core, there are provided pins 48 orsimilar holding devices that rotate together with the winding core. Theendless hollow fiber is wound about one of these pins 48 and fixatedbefore winding of the second hollow fiber 56 begins.

As becomes apparent from what has been said herein above, winding iscarried out with an endless hollow fiber, although the module isdescribed for the state in which the module is completed as shown inFIG. 1. In this state, one obtains a plurality of discrete hollow fibersby winding the one endless hollow fiber. This happens by cutting theexcess regions of the hollow fibers at the axial ends of the windingcore. It is not before this cutting has been performed that the interiorof the discrete hollow fibers becomes accessible at the axial ends,meaning that the inlet 20 and outlet 22 are formed. This will bediscussed in greater detail herein after.

FIG. 5 shows how the second hollow fiber 56 of the first layer 40 islaid down; for this purpose, the direction of rotation of the windingmachine is changed, the second hollow fiber 56 is laid down beside thealready laid down first hollow fiber 54 in the clearance position atherefrom.

To lay down the third hollow fiber 58, see FIG. 6, the fiber is againfirst laid down so as to form a grip around a fixed point, morespecifically a pin 48, but this time at the other axial end. Next, thethird hollow fiber 58 is laid down. This procedure is repeated until thefirst layer 40 is completely filled. Then, the second layer 42 is laiddown. With each layer that is laid down, the winding gains in stability.The winding more specifically gains mechanical strength by the plasticrings 24 mounted to its axial ends.

It is possible to concurrently wind two endless hollow fibers, as shownin FIG. 7. It is also possible to simultaneously supply further hollowfibers in parallel. In the illustration as shown in FIG. 7, twodiscrete, endless hollow fibers are supplied to the winding core fromtwo different sides, that is, that are offset by 180°, in order toaccommodate the radial components of the tensile strains of the twoendless hollow fibers and, accordingly, for the winding core to beprevented from bending with respect to its axis.

Herein after, the distribution of the discrete hollow fibers of onelayer within said layer will be discussed. In FIG. 8, whichsubstantially corresponds to FIG. 6, the clearance a betweenneighbouring hollow fibers and the outer diameter d of the hollow fibersis shown. FIG. 9 illustrates how the three hollow fibers are arrangedabout the circumference of the winding core, which is here formed by atube 32. The tube 32 thereby has the outer diameter Dk. The length ofthe circumferences accordingly is π·Dk; n1 hollow fibers have to beaccommodated along this length, with the hollow fibers being laid downat the wind angle .alpha. In the sectioning plane of FIG. 9 and also atthe axial ends, meaning in the region of the outlet 22 and of the inlet20, the hollow fibers appear to be ellipses because of the wind angle.In FIG. 9, there is indicated the distance 1 by which a hollow fiber 58has to be displaced in the radial plane in the circumferential directionin order to reach the site of the neighbouring hollow fiber. In thefirst layer considered herein, a total of n1 hollow fibers are in aclearance relationship a1 with each other. Accordingly, the followingequation is obtained:n1·(a1+d)=Dk·π·cos α  (1).

In a second layer, which receives n2 hollow fibers, the clearancebetween neighbouring hollow fibers is a2. The imaginary cylinder of thissecond layer has the diameter Dk+2 d. The following relation isobtained:n2·(a2+d)=(Dk+2d)π·cos α  (2).

The same applies in equivalent fashion to the other windings. Theclearance a between neighbouring hollow fibers should be, as far aspracticable, the same for the discrete windings, and should preferablyvary by less than 30%, more specifically by less than 20% and preferablyby less than 10% from one layer to the other. It is possible to workwith the same constant clearance a for all of the layers if thefollowing relationship is respected:n2−n1=2d π cos α:(a+d)  (3).

This equation (3) has been obtained by substituting a for a1 and a2respectively in the equations (1) and (2) and by subtracting equation(2) from equation (1). As a matter of course, n1, n2 and so on arenatural numbers so that the difference obtained by subtracting thenumber of hollow fibers in the second layer from the number of hollowfibers in the first layer will also be a natural number, for example 1or 2. By selecting the wind angle .alpha., the clearance a and the outerdiameter d of the hollow fibers, one obtains a winding in which theclearance a is the same in all of the layers.

It appears from the equations (1) through (3) indicated herein abovethat, if n, meaning the number of hollow fibers in one layer, and D,meaning the diameter of the imaginary cylinder of the layer, are highenough, the constructor is still free to determine suited clearances a.

FIG. 9 shows the arrangement of the only three hollow fibers of FIG. 8on the tube, said tube forming with its outer shell the imaginarycylinder 35 of the first layer. A dotted line with a diameter Dk+d isalso shown in FIG. 9, the centerpoint of the various hollow fibers lyingon said line. Further, an imaginary cylinder 36 that forms the end ofthe first layer and defines the wind diameter for the second layer thathas not been illustrated herein is also shown.

These dispositions are illustrated in still closer detail in FIG. 10which is a sectional view of a module having three layers 40, 42, 44.All the layers are fully occupied by hollow fibers. The second layer 42is located directly on top of the first layer 40 and is bounded on itsinner side by the imaginary cylinder 36 of the second layer. Likewise,the third layer 44 is bounded on its inner side by the cylinder 37. Anadditional cylinder 39 is shown, which bounds a possibly provided fourthlayer on the inner side thereof. If no fourth layer were provided, theorientation of 39 would indicate the orientation of an outer shell 34 inthe ideal case, that is, with no well in the region of the helicalchannels 38.

Moreover, in accordance with the invention, the cross section availablefor the flow path of the gas to be dried and for the flow path of thecirculation gas may also be adapted and adjusted with respect to eachother. This is explained with reference to FIG. 12. As shown in FIG. 12,one has, for every single hollow fiber, an overall inner surface Ai thatis determined by the square of the inner radius times 71 and an overallouter surface Aa that is determined by the surface of the rectangle(d+a)·d minus the entire cross section of a hollow fiber, i.e., (d/2)²·π. A judicious selection of a in particular, but also of the otherparameters, permits to selectively obtain the desired relationshipbetween the inner flow path and the outer flow path. The velocity of theflows is also to be taken into consideration. A ratio of the inside flowvelocity to the outside flow velocity ranging from 1-5 is of practicalimportance depending on the desired degree of drying or on the desiredreduction in the dew point. The respective volume flows are obtained bymultiplying the products of the flow velocity with the availablecross-sectional area. Usually, one works with a circulating air volumeflow on the order of some percents of the volume flow of air to bedried, for example about 12% thereof. The above considerations permit tocalculate a suited cross section ratio of Aa to Ai and then, to set a, dand the wind angle .alpha. as well as, in addition thereto, D, by meansof the parameters.

Upon completion of the winding consisting of the discrete layers 40, 42,and so on, said winding is stabilized by plastic rings 24 applied totheir ends, with this latter step being performed according to priorart. A particularly advantageous fact for introducing plastic materialinto the spaces between the hollow fibers is that radial permeabilityexists, that said permeability is a known variable and that; in additionthereto, it is homogeneous.

Referring to the FIGS. 13-15, details regarding the manufacturingprocess, meaning more specifically the winding of a fiber, will bediscussed herein after.

The FIGS. 13 and 14 show how a hollow fiber 54 is laid down onto thecylinder 35 or the tube 32 of the first layer 40, what will be saidapplying also to the laying down of the other layers 42, 44, and so on.In a winding machine that is shown only schematically herein, the tube32 is rotated about the module axis 30 in the direction of the arrow.The hollow fiber 54 extends tangentially and at a wind angle .alpha.towards the tube 32. It passes through an orifice 60 in the fiber thatprovides for precision guiding and, as a result thereof, accuratepositioning of the hollow fiber 54 in both directions in space. Theorifice 60 in the fiber is moved in the direction of the module axis 30relative to the tube 32 or of the already built-up portion of thewinding., The movement occurs pursuant to arrow 62 at the velocityresulting from the geometry chosen for the winding, more specificallyfrom the wind angle .alpha. and the diameter of the tube 32.

The hollow fiber 54 is supplied from a stock that has not beenillustrated herein to the orifice 60 of the fiber. This is symbolized bythe arrow 64. Before the hollow fiber 54 reaches the orifice 60 of thefiber, it is conducted over a first deflector roll 66 where it isdeviated downward toward a dancer roll 68 and from there upward to asecond deflector roll 70 that more specifically is built according tothe same design principle as the first deflector roll and is disposedapproximately on the same vertical height as the latter.

The dancer roll 68 has a given weight. As a result, in the feed portionand in the discharge portion of the hollow fiber, there prevails amechanical tensile force in the hollow fiber on the left and on theright side of the dancer roll 68 in FIG. 13. Further, the dancer roll 68further accommodates in a known manner fluctuations in the hollow fibersupply from the stock. It ensures that the tension in the fiber remainsconstant.

Typically, the dancer roll has a weight ranging between 10 and 200 g,for example of 100 g. As a result, the tension in the thread betweendancer roll 68 and tube 32 is about 50 g.

The mechanical strain in the hollow fiber 54 causes the hollow fiber toslightly stretch, said stretch serving to wind the hollow fiber 54 ontothe tube 32. As a result, the hollow fiber 54 rests on the tube 32 or,in the second layer 42, on the fibers of the first layer 40 and in thethird layer 44 on the fibers of the second layer 42 and so on, with africtional fit.

A strong winding is achieved thanks to the strain, respectively thestretch. The discrete hollow fibers 54, 56, 58 can only be displaced inthe direction of the module axis 30, that is, be pushed out of the idealhelical line on which they were laid during winding by exerting acertain force. As a result of the stretch, conscious or inadvertentdeflection of a fiber causes the latter to return to its initial statewhen the deflecting force is eliminated.

The strain in the hollow fibers is to be selected such that a strongwinding is achieved. As can be seen, the wind angles are in a range suchthat each fiber is wound at least once between inlet 20 and outlet 22,meaning is wrapped at least 360° around the tube 32. Under thesecircumstances, sufficient frictional hold of the discrete fibers on thetube 20 or on the underlying layer is important in achieving a strongwinding. A deformation also occurs.

But the strain in the discrete hollow fibers is not allowed to become sohigh as to cause the hollow fibers to noticeably vary theircross-sectional shape. The weight of the dancer roll 68 is chosen inaccordance with the physical properties of the fiber 54 to cause thehollow fibers to deform within tolerable limits;

FIG. 15 shows small details of three consecutive layers 40, 42 and 44.The wind angle is 45° so that the hollow fibers 54, 56 and 58 intersectat an angle of 90°. It appears that the hollow fibers 56 of the secondlayer 42 slightly deform at the points of touching contact with thehollow fibers 54 of the first layer 40 and with the hollow fibers 58 ofthe third layer 44, with the deformation regions being labelled at 72.In the deformation regions 72, the cross-sectional shape differs fromthe ideal circular shape.

On the one side, deformation is necessary to achieve a strong winding,on the other side however it is disadvantageous because it results insome places having a slightly smaller free cross-section than thoselocated outside of the deformation regions. The deformation regions 72are selected to be just large enough to allow positioning of the hollowfibers with respect to one another while keeping the variation incross-section low, more specifically below 10%, preferably below 5% andmore specifically below 2%.

A particularly advantageous embodiment of the invention will now bediscussed with reference to FIG. 16. Instead of laying down on a windingcore 32 a winding for one single module, one relatively long winding theaxial length of which is sufficient for a plurality of discrete modulesis produced. Whilst the discrete modules have a length of for example10-40 cm, it is readily possible to produce quite long windings, of forexample 4 m long. These windings are implemented in exactly the samemanner as described herein above for a winding of one single module. Thecompleted preform 50 is potted at desired intervals with a sealingcompound or encapsulated with plastic rings 24, as illustrated in FIG.12. The plastic rings 24 are sectioned in their central region, seesectioning plane 52, with inlet 20 and outlet 22 being formed at thesame time so as to obtain the discrete modules. It is also possible touse mechanical clamps or the like instead of the plastic rings 24.

In the implementation as shown in FIG. 16, the way of producing thewinding is of no concern. Meaning, any winding will do. It needs not beimplemented as set forth in patent claim 1. Any shape in arranging thehollow fibers will do to first produce, in accordance with the proposal,a quite long preform 50 that will later be divided into discrete moduleparts. The plastic rings are obtained by injecting a plastic material orany other suited material.

1-10. (canceled)
 11. A hollow fiber fluid separation module comprising:an inlet for an inlet feed flow, an outlet for an exit flow; an accessport for a permeate flow, a discharge port for the permeate flow, amodule axis and a plurality of hollow fibers; each of the fibersextending from the inlet to the outlet and comprising an interiorcommunicating with the inlet at one end of each hollow fiber and withthe outlet at the other end of each hollow fiber, with the hollow fibersbeing wound in multiple layers to form a hollow cylindrical coil; eachlayer being defined on its inner side by an imaginary cylinder andhaving a number of hollow fibers helically wound on the cylinder with ahelix angle .alpha.; the fibers being in a clearance relationship witheach other and equally spaced on the cylinder, with one layer differingfrom a neighbouring layer by the fact that all the fibers of the onelayer are inclined at the wind angle plus .alpha. whereas all the fibersof the neighbouring layer are at the wind angle minus .alpha.; and eachfiber being wrapped 360° at least once around the associated cylinderand being laid down during winding with a tensile strain high enough forthe fiber to be frictionally held in the best possible manner to thecrosswise disposed fibers lying underneath and low enough for the hollowfibers not to have their inner cross section noticeably restricted eventhough they are deformed at the intersections and for all of the hollowfibers to be applied with the same tensile strain.
 12. The hollow fiberfluid separation module as set forth in claim 11, wherein the first,lowermost layer is located on a tube that forms the imaginary cylinderof the layer.
 13. The hollow fiber fluid separation module as set forthin claim 11, wherein the access port comprises at least one axial borethat is formed in the tube.
 14. The hollow fiber fluid separation moduleas set forth in claim 11, wherein the wind angle .alpha. ranges between15° and 75°.
 15. The hollow fiber fluid separation module as set forthin claim 11, wherein the distance a between two hollow fibers of onelayer ranges between onefold and tenfold the inner radius of the hollowfibers.
 16. The hollow fiber fluid separation module as set forth inclaim 11, wherein all of the fibers have the same length.
 17. The hollowfiber fluid separation module as set forth in claim 11, wherein all ofthe fibers are built according to the same design principle.
 18. Thehollow fiber fluid separation module as set forth in claim 11, whereinthe tensile strain is selected such that the free inner cross section ofthe hollow fiber at the intersections is more than 90%, morespecifically more than 95% and advantageously more than 98% of the innercross section of the hollow fiber outside of the intersections.
 19. Thehollow fiber fluid separation module as set forth in claim 11, whereinthe outermost layer of the winding is enclosed by a shell that tightlysurrounds the outermost layer and comprises access or exit means forpermeate flow, more specifically for circulation gas.
 20. The hollowfiber fluid separation module as set forth in claim 11, wherein themodule is obtained from a preform by cutting the preform along thesectioning planes and that the preform comprises an axially quite longwinding and has an axial length that is greater than the length of aplurality of modules.